Heat-sensitive adhesive sheet and information recorded material using the same

ABSTRACT

A heat-sensitive adhesive sheet for bonding a pair of information-recorded faces, belonging to the same sheet or two different sheets of recording material, together by application of heat thereto, which comprises three or more layers, including a support and a synthetic resin layer coated on either side of the support, having a peeling resistance ranging from 10 to 150 g/50 mm between the support and each synthetic resin layer in the T-peel test performed at a peeling speed of 300 mm/min. in the atmosphere of 20° C. and 65% RH, and a peeling resistance greater than 300 g/50 mm, measured under the same conditions as described above, between each synthetic resin layer and the information-recorded face when heated in a condition wherein the adhesive sheet is sandwiched in between a pair of information-recorded faces of the recording material, and an information-recorded material, preferably of postcard size which is made by inserting the foregoing heat-sensitive adhesive sheet between each pair of information-recorded faces belonging to one sheet or two or more sheets of recording material, wherein at least two information-recorded faces are present, and then by heating them at a temperature of 100° C. or lower to unite them together through heat-sensitive adhesion.

FIELD OF THE INVENTION

This invention relates to heat-sensitive adhesive sheet which enable onepair of information-recorded faces of one or two sheets of recordingmaterial to adhere to each other with the capability of peeling apartfrom each other when needed, and information-recorded materialsutilizing said heat-sensitive adhesive sheets. In particular, it isconcerned with a heat-sensitive adhesive sheet and aninformation-recorded material utilizing said adhesive sheet(s) which canbe used for communicating more information than conventional postcards.

BACKGROUND OF THE INVENTION

In recent years, the occasion of mailing various kinds of documents onprivacy of individuals, e.g., bills, notices for payment, receipts andnotices for expiration which relate, e.g., to taxes, annuities, bonds,deposits and savings, credits, telegram and telephone charges, gascharge, water charge, electricity charge and so on, has markedlyincreased in number.

In mailing documents regarding privacy of each individual, sealedletters have so far been used from the standpoint of protecting privacy.However, mailing documents by sealed letter has the demerit of highprice, compared with mailing documents by postcard.

Under these circumstances, various types of postcards capable of keepingthe contents of a private message secret have been proposed in recentyears.

As one of these proposals, a paper seal which is applied to the surfaceof a conventional postcard, on letters and figures are recorded, havinga peel-apart possibility in order to temporarily veil the contents ofthe record. In the paper seal of this kind, a weak tackifier is used toform its adhesive face, so it is necessary to laminate a release paperfor the protection of the weak tackifier layer. The use of a releasepaper is disadvantageous in that it causes an increase in cost, and isattended with a trouble of its disposal. Moreover, the paperseal-applied postcard has the defect that part of the letters and thelike written on a postcard is stripped off and transferred to the weaktackifier layer in peeling the paper seal off the postcard; making hardto read. What is worse, the paper seal can be delaminated andrelaminated so as not to leave traces of taking off the seal.Accordingly, the paper seal suffers another defect in that it isinferior for protecting against invasion of privacy.

As another material, there can be cited a label of the type which is asheet lined with aluminum foil, applied to the letters-written side of apostcard in order to screen the message on the postcard, and designed sothat breaking the seal becomes possible only when the sheet is cut openalong perforations hemming round the postcard.

However, this label is expensive because it is a laminate having acomposite structure and, what is worse, it is hard to break into piecesand to destroy by fire. Therefore, it suffers from a disposal problem.

In addition, the foregoing paper seal and label can be used only forveiling the recorded information. Accordingly, there has been no othermeans of mailing a great deal of information but to adopt the procedureof mailing in sealed covers which is higher in price.

In order to solve the above-described problems, we have previouslyproposed a transparent heat-sensitive adhesive sheet having adhesivenesson both sides (Jitsuyo Kokai No. 02-25546, wherein the term "JitsuyoKokai" used means an "unexamined published Japanese utility modelapplication"). By the use of this sheet, the information-recorded facesof two sheets of postcard-size recording material can be bonded togetherin a condition whereby they can be peeled apart from each other whennecessary.

However, it is essential for the process of manufacturing the foregoingtransparent heat-sensitive adhesive sheet to involve a step of providinga thermoplastic resin layer on one side of a transparent plastic sheetin a releasable condition using a fusion extrusion technique. This stepmakes the manufacturing process complicated. In addition, not only thetransparent plastic sheet but also the thermoplastic resin layer formedby fusion extrusion are hard to break into pieces by hand, so it isnecessary to dispose of the information-recorded material using aspecial disposer such as a shredder from the standpoint of keeping theinformation secret. Disposal of this sort is inconvenient for privatemails. Moreover, a transparent material is used as the support of saidtransparent adhesive sheet so that the information recorded on the facewhere the support remains can be read since the support is left on oneof the information-recorded faces when the information-recorded materialis torn open. This causes according to the quality of the recordingmaterial a serious situation that the secrecy of the informationrecorded inside the recording material is not preserved to asatisfactory extent.

On our further examination, it has been found that an entirelysatisfactory result can be obtained by using a heat-sensitive adhesivesheet which has a support and synthetic resin layer provided on eachside thereof in a condition that it can be peeled apart therefrom ifneeded, with the synthetic resin layer having an ability to adhere to aninformation-recorded face in a substantially unreleasable condition whenheat is applied thereto, thus achieving this invention.

SUMMARY OF THE INVENTION

Therefore, a first object of this invention is to provide aheat-sensitive adhesive sheet which enables a pair ofinformation-recorded faces of recording material(s) to bond together ina condition such that it can be peeled apart therefrom at the time it isdue.

A second object of this invention is to provide a heat-sensitiveadhesive sheet which can be produced with ease and at a low price,enables the recording materials, to which this adhesive sheet was onceapplied, to be recycled, and has an excellent capability for keepingrecorded information secret.

A third object of this invention is to provide an information-recordedmaterial which can be disposed of easily without using any specialdisposer, and has an excellent ability to protect the privateinformation against disclosure.

A fourth object of this invention is to provide a post card which cancommunicate more information than conventional ones, and is superior inprotecting against invasion of privacy.

The above-described objects of this invention are attained with aheat-sensitive adhesive sheet for bonding a pair of information-recordedfaces of one or two sheets of recording material together by applicationof heat thereto, and with an information-recorded material using one ormore of said heat-sensitive adhesive sheet; said heat-sensitive adhesivesheet comprising three of more constituent layers including a supportand synthetic resin layers coated on both sides of the support, whereinthe support and the synthetic resin meet the conditions that the peelingresistance between the support and each synthetic resin layer in theT-peel test (ASTM D1876-61T) ranges from 10 to 150 g/50 mm when measuredat a peeling speed of 300 mm/min. in the atmosphere of 20° C. and 65%RH, and the peeling resistance between each synthetic resin layer andthe information-recorded face in the T-peel test becomes greater than300 g/50 mm, measured at a peeling speed of 300 mm/min in the atmosphereof 20° C. and 65% RH, when said adhesive sheet is sandwiched in betweeneach pair of the information-recorded faces of the recording material(s)and heat is applied thereto.

In accordance with embodiments of this invention, the present adhesivesheet, in contrast to conventional transparent heat-sensitive adhesivesheets applied to information-recorded materials, enables its support tobe separated from the information-recorded material(s) when theinformation-recorded faces bonded together through the adhesive sheetare peeled part from each other so that information recorded inside canbe read. Consequently, it becomes feasible to use as the support anopaque material or a light absorbing material, which makes it impossibleto look through the recorded information from the outside, that is tosay, which results in heightening the concealing ability of the presentadhesive sheet.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of the adhesive sheet of thisinvention.

FIG. 2 is a cross-sectional view of the information-recorded material ofthis invention wherein the adhesive sheet of this invention is used.

FIG. 3 is an example of a recording material which can be made into theinformation-recorded material of this invention by being folded into theS-form.

FIG. 4 is another example of a recording material which can be made intothe information-recorded material of this invention by being folded intothe Z-form.

FIG. 5 is a cross-sectional view of the information-recorded materialusing the recording material illustrated in FIG. 4.

In the Figures, an adhesive sheet is denoted by 3, a support by 3a, asynthetic resin layer by 3b, a recording material by 5, andinformation-recorded faces by 5a and 5b.

DETAILED DESCRIPTION OF THE INVENTION

The heat-sensitive adhesive sheet of this invention (abbreviated as "theadhesive sheet", hereinafter) and the information-recorded materialsusing said adhesive sheet are described in detail on the basis of thefigures. However, the invention should not be construed as being limitedto such figures.

A cross-sectional view of the adhesive sheet of this invention is shownin FIG. 1, and that of the information-recorded material of thisinvention in which the adhesive sheet of FIG. 1 is used is shown in FIG.2.

In these figures, (3) stands for the adhesive sheet of this invention,(3a) stands for a colorless or colored, transparent or opaque support,and (3b) stands for a synthetic resin layer formed by coating asynthetic resin on either side of the support (3a).

The support (3a) can be chosen properly from among paper; transparentsynthetic resin films which may be opacified by containing a lot ofvoids or white pigments therein, by providing a white coat on the filmsurface or by evaporating a metal into a thin layer on the film surface;composite materials made up of paper, such as impregnated paper (made bypercolating a resin solution into paper layers and drying them to cake);and plastics, or other known materials. However, it is preferable to usean opaque support in order to make it impossible to look through theinformation recorded inside the recording material. Therefore, it isdesirable in particular to color the above-cited paper or film sheetswith a dye or pigment to impart a light-absorbing capability to them.Although such a dye or pigment can be chosen properly from knownmaterials, those of black color are particularly preferred from thestandpoint of ensuring the secrecy of the recorded information beforeopening. Dyes or pigments may each be used alone or as a mixture of twoor more thereof, or dyes and pigments may be used together. Thesecoloring agents can be coated on the support (3a), or incorporated intothe support (3a) using known methods.

In using a synthetic resin film as the support (3a), an optimal one isselected from known synthetic resin films including polyethylene film,polypropylene film, polyester film, cellulose triacetate film,polycarbonate film, polyamide film, and so on.

In order to form the synthetic resin layer (3b), a synthetic resinhaving in the T-peel test a peeling resistance of 10-150 g/50 mm withrespect to the support (3a), and a peeling resistance of 300 g/50 mm ormore with respect to the information-recorded face when measured at thepeeling speed of 300 mm/min in the atmosphere of 20° C. and 65% RH isused. Consequently, the application of the adhesive sheet(s) of thisinvention to an information-recorded material enables easy peeling ofthe support (3a) from the recorded material at the time of opening.

Synthetic resins used for the synthetic resin layer (3b) of thisinvention can be chosen properly from among known materials, includingacryl resins, vinyl chloride/vinyl acetate copolymer resins, polyesterresins, vinyl chloride/vinyl propionate copolymer resins, polyvinylformal resins, polyvinyl butyral resins, polyolefin resins, and mixturesof two or more of the above-cited ones. In particular, those resinshaving a glass transition point of 25° C. or higher are preferred fromthe standpoints of facility in peeling apart from the support and theirsuperiority in keeping quality (cf. Example 1 and Comparative Example1). Among the synthetic resins of such a kind, polyolefin resindispersions, especially those of ethylenic olefin copolymerized resins,low density polyethylenes, vinyl acetate-olefin copolymers, ionomerresin and so on, and mixtures of two or more of these resin dispersions,are favored over others. In particular, those having a Vicat softeningtemperature of 45° C. or higher are advantageous in that they can ensurefurther facility in peeling apart from the support and better keepingquality (cf. Example 2 and Comparative Example 2). As specific examplesof resin mixtures which can be preferably used, mention may be made ofcompositions obtained by mixing one(s) selected from dispersions ofethylenic olefins copolymerized resins, low density polyethylenes, vinylacetate-olefin copolymers or ionomer resins with self-emulsifyingpolyolefin resin(s) in a mixing ratio of from 95/5 to 5/95 on a resinsbasis. When these compositions are coated and dried, synthetic resinlayers having a Vicat softening temperature of 45° C. or higher can beformed (cf. Example 3 and Comparative Example 3). The term "Vicatsoftening temperature" used herein is referred to as a temperaturemeasured in accordance with ASTMD 1525-70, and has the same meaning asVicat softening point. More specifically, it is represented by thetemperature at which the stylus point of a gauge is penetrated below thesurface of plastics at a depth of 1 mm when the gauge on which a load of1 Kg is imposed is placed on the plastics surface, and heat is appliedthereto.

A dry thickness of a synthetic resin coat is preferably 20 μm or lessfor facilitating destruction. In particular, a synthetic resin coatdesigned so as to have a dry thickness of about 10 μm or less is favoredbecause it can be easily broken into pieces by hand.

In addition, an adhesive layer may be provided between the syntheticresin coat (3b) and the support (3a), if desired.

As described above, the adhesive sheet (3) of this invention isconstituted by at least three layers, namely a support (3a) andsynthetic resin coats (3b) provided on both sides of the support.Information-recorded materials using the adhesive sheet (3) of thisinvention are described in detail below.

An information-recorded material relating to this invention is referredto as one which is obtained by sandwiching the adhesive sheet (3) ofthis invention in between each pair of information-recorded faces (5a,5b), whether present on the same sheet or different sheets of recordingmaterial, wherein at least two or more information-recorded faces mustbe present in all, and then by heating them to a temperature of 100° C.or below to unite them together.

A recording material (5) used in the information-recorded material ofthis invention can be chosen properly from known materials, includingordinary paper used for postcards, letter paper, and recording materialsfor computer use.

More specifically, the information-recorded material of this inventionis a postcard-size material formed by sandwiching the adhesive sheet (3)of this invention in between every pair of information-recorded faces(arranged opposite to each other) of recording material(s) (5), and thenby heating them at a temperature of 100° C. or below to unite themtogether. As shown in FIG. 2, for instance, two sheets of postalcard-size recording material (5) are arranged so that their respectiveinformation-recorded faces (5a and 5b) oppose each other andtherebetween is sandwiched in the foregoing adhesive sheet (3), which isfollowed by uniting them in one together through heat-sensitiveadhesion. On the other hand, as shown in FIG. 3 and FIG. 4, a recordingmaterial (5) having an amount of information sufficient for three faceswhich has been recorded simultaneously on at least one side of one sheetof printing paper is folded in the S-form (FIG. 3) or in the Z-form(FIG. 4), and the adhesive sheet (3) is sandwiched in between each pairof opposite faces (5a and 5b), followed by uniting them (See FIG. 5). Inthe latter case, much more information can be incorporated in a postcardsince it becomes feasible to have four information-recorded faces insidethe postcard.

In the above description, a special case in application of the adhesivesheet of this invention, that is, application to a postcard, is takenup. However, the adhesive sheet of this invention can be used forvarious purposes as well as postcards. As an example of such purposes,mention may be made of an information-recorded material to be insertedinto an envelope. More specifically, when the adhesive sheet (3) of thisinvention is sandwiched in between the opposite information-recordedfaces (5a and 5b) of a twofold recording material (5) and subjected toheat-sensitive adhesion, the information recorded inside the recordingmaterial can be kept secret even if the sealed letter is opened so as toleave no traces of breaking the seal, and the contents of documentsinserted in the envelope cannot be looked through from the outside.Therefore, the mailing in the above-described form is superior forprotecting against invasion of privacy in comparison to the mailing inthe form of a conventional sealed letter.

As described above in detail, the present adhesive sheet can be producedwith ease at a low price since the manufacturing process consists offewer steps, compared with conventional transparent heat-sensitiveadhesive sheets.

In addition, a postcard-size recording material utilizing the adhesivesheet(s) of this invention can keep the secrecy of its contents, and cancommunicate more than twice the quantity of information by the samepostage as that of a conventional postcard. Further, theinformation-recorded material can be easily torn to pieces with ease andthrown away at the time of disuse, so the disposal thereof can be donewith ease even at home. Therefore, the information-recorded material towhich the adhesive sheet(s) of this invention is(are) applied is usefulin particular as the means of communicating private information whichrequires secrecy. Furthermore, it can be recycled since the support ofthe adhesive sheet can be disposed of separately.

EXAMPLE

Now, the present invention will be illustrated in more detail byreference to the following examples. However, the invention should notbe construed as being limited to these examples.

EXAMPLE 1

On each side of a 16 μm-thick polyester film support (3a), a transparentpolyvinyl butyral resin having a glass transition point of 57° C. andcapable of adhering to an information-recorded material when heated to80° C. was coated to a dry thickness of 10 μm to prepare an adhesivesheet relating to this invention.

Then, a recording material intended for postcard use, which had a basisweight of 80 g/m² on which information from a computer was recorded inadvance, was folded, as shown in FIG. 3, along the dashed line P so thatthe information-recorded face might be brought into face-to-facecontact, and further folded back along the dashed line O.

The previously prepared adhesive sheet was sandwiched in between eachpair of the opposite faces of the folded material, and passed between apair of hot rolls having a surface temperature controlled to 100°-110°C. to effect heat-sensitive adhesion, followed by thorough cooling (SeeFIG. 5).

The thus prepared postcard was able to be delaminated with ease at theinterface between the support (3a) and each coat of the synthetic resin(3b). In addition, the printed faces suffered no damage and the recordedinformation was able to be read satisfactorily. Additionally, thisinformation-recorded material was examined for peeling resistanceaccording to the T-peel test performed at a peeling speed of 300 mm/minunder the atmosphere of 20° C. and 65% RH. As the result thereof, it hadthe peeling resistance of 40 g/50 mm between the support (3a) and eachsynthetic resin coat (3b), and that of 300 g/50 mm between theinformation-recorded material and the adhesive sheet of this invention.

The whole weight of the postcard prepared in the above-described mannerwas confirmed to meet the standard in the postal regulations, that is,to be usable as a postal card.

COMPARATIVE EXAMPLE 1

An adhesive sheet was prepared in the same manner as in Example 1,except that an acryl resin having a glass transition temperature of 20°C. was coated as the synthetic resin coat (3b). The obtained sheet wassimilarly applied to the information-recorded material.

The peeling resistance of the adhesive sheet applied material wasexamined by the T-peel test under the same condition as in Example 1.The result was that the peeling resistance, though the same as inExample 1 (that is, 300 g/50 mm) between the information-recordedmaterial and the adhesive sheet, was 200 g/50 mm between the support andthe synthetic resin coat (3b), resulting in peel-apart curling.Accordingly, it was difficult to read the printed letters and figures.

EXAMPLE 2

On each side of a 16 μm-thick polyester film support (3a), into which alight absorbing black pigment was previously kneaded, a transparentethylenic olefins-copolymerized resin having a Vicat softeningtemperature of 54° C. and capable of adhering to an information-recordedmaterial when heated to 90° C. was coated to a dry thickness of 10 μm toprepare an adhesive sheet relating to this invention.

Then, the thus prepared adhesive sheet was sandwiched in between eachpair of opposed faces of an information-recorded material in the sameway as in Example 1, and passed between a pair of hot rolls having asurface temperature controlled to 100°-110° C. to effect heat-sensitiveadhesion, followed by thorough cooling (See FIG. 5).

The thus prepared postcard was able to be delaminated with ease at theinterface between the support (3a) and each coat of the synthetic resin(3b). In addition, the printed faces suffered no damage and the recordedinformation was able to be read satisfactorily. Additionally, thisinformation-recorded material was examined for peeling resistanceaccording to the T-peel test performed under the same condition as inExample 1. As the result thereof, it had the peeling resistance of 60g/50 mm between the support (3a) and each synthetic resin coat (3b), andthat of 300 g/50 mm or more between the information-recorded materialand the adhesive sheet of this invention.

The whole weight of the postcard prepared in the above-described mannerwas confirmed to meet the standard in the postal regulations, that is,to be usable as a postal card.

COMPARATIVE EXAMPLE 2

An adhesive sheet was prepared in the same manner as in Example 2,except that a vinyl acetate-olefin copolymerized resin having a Vicatsoftening temperature of 42° C. was coated as the synthetic resin coat(3b). The obtained sheet was similarly applied to information-recordedmaterial.

The peeling resistance of the adhesive sheet-applied material wasexamined by the T-peel test under the same condition as in Example 2.The result was that the peeling resistance, though similar to that inExample 2 (that is, 300 g/50 mm) between the information-recordedmaterial and the adhesive sheet, was 200 g/50 mm between the support andthe synethetic resin coat (3b), thereby causing peel-apart curling.Consequently, it was difficult to read the printed letters and figures.Further, the thus curled-up material was kept for 30 days in theatmosphere of 30° C. and 65% RH. Thereupon, a blocking phenomenon wasobserved. This result demonstrates the inferiority of the comparativesheet in keeping facility.

EXAMPLE 3

On each side of a 16 μm-thick polyester film support (3a), into which alight-absorbing black pigment was previously kneaded, a resinouscomposition capable of adhering to an information-recorded material whenheated to 80° C., which was a mixture of a dispersion of an ethylenicolefins-copolymerized resin having a Vicat softening temperature of 54°C. and a self-emulsified polyolefin resin having a Vicat softeningtemperature of 83° C. with a mixing ratio of 60/40 on a solids basis,was coated to a dry thickness of 10 μm to prepare an adhesive sheetrelating to this invention.

Then, a recording material intended for postcard use, which had a basisweight of 80 g/m² on which information from a computer was recorded inadvance, was folded, as shown in FIG. 3, along the dashed line P so thatthe information-recorded face might be brought into face-to-facecontact, and further folded back along the dashed line O.

The adhesive sheet prepared in advance was sandwiched in between eachpair of the opposite faces of the folded material, and passed between apair of hot rolls having a surface temperature controlled to 100°-110°C. to effect heat-sensitive adhesion, followed by thorough cooling (SeeFIG. 5).

The thus prepared postcard was able to be delaminated with ease at theinterface between the support (3a) and each coat of the synthetic resin(3b). In addition, the printed faces suffered no damage and the recordedinformation was able to be read satisfactorily. Additionally, thisinformation-recorded material was examined for peeling resistanceaccording to the T-peel test performed at a peeling speed of 300 mm/minunder the atmosphere of 20° C. and 65% RH. As the result thereof, it hadthe peeling resistance of 90 g/50 mm between the support (3a) and eachsynthetic resin coat (3b), and that of 300 g/50 mm between theinformation-recorded material and the adhesive sheet of this invention.

The whole weight of the postcard prepared in the above-described mannerwas confirmed to meet the standard in the postal regulations, that is,to be usable as a postal card.

COMPARATIVE EXAMPLE 3

An adhesive sheet was prepared in the same manner as in Example 3,except that a dispersion of a vinyl acetate-olefin copolymerized resinhaving a Vicat softening temperature of 42° C. was coated as thesynthetic resin coat (3b). The obtained sheet was similarly applied tothe information-recorded material.

The peeling resistance of the adhesive sheet-applied material wasexamined by the T-peel test under the same condition as in Example 3.The result was that the peeling resistance, though similar to that inExample 3 (that is, not less than 300 g/50 mm) between theinformation-recorded material and the adhesive sheet, was 200 g/50 mmbetween the support and the synthetic resin coat (3b), thereby causingpeel-apart curling. Consequently, it was difficult to read the printedletters and figures. Additionally, a blocking phenomenon was observed bykeeping the thus curled-up material for 30 days in the atmosphere of 30°C. and 65% RH, which demonstrated the inferiority of the comparativesheet in keeping facility.

Thus, the foregoing examples of this invention and those for comparisonhave proved that desirable characteristics are attained when thesynthetic resin coat (3b) has a glass transition point of 25° C. orhigher, particularly a Vicat softening temperature of 45° C. or higher.

What is claimed is:
 1. A heat-sensitive adhesive sheet for bonding apair of information-recorded faces of one or two sheets of recordingmaterial together by application of heat thereto, said adhesive sheetcomprising:an opaque support layer having two sides, a synthetic resinlayer coated on one side of said opaque support layer, and anothersynthetic resin layer coated on the other side of said opaque supportlayer, each of said synthetic resin layers having a peeling resistanceof 10-150 g/50 mm between said opaque support layer and each of saidsynthetic resin layers in a T-peel test performed at a peeling speed of300 mm/min. in an atmosphere of 20° C. and 65% RH, said synthetic resinlayers capable of exhibiting peeling resistance greater than 300 g/50mm, measured under the same conditions as said T-peel test, between eachof said synthetic resin layers and an information-recorded face of arecording material, and each of said synthetic resin layers having aglass transition temperature of at least 25° C. and a Vicat softeningtemperature of at least 45° C.
 2. A heat-sensitive adhesive sheet ofclaim 1, wherein said support layer is a light-absorbing sheetcontaining a dye, a pigment, or both.
 3. A heat-sensitive adhesive sheetof claim 1, wherein each of said synthetic resin layers has a thicknessof at most 20 μm.
 4. A heat-sensitive adhesive sheet of claim 1, whereineach of said synthetic resin layers contains a resin selected from thegroup consisting of acryl resins, vinyl chloride-vinyl acetatecopolymerized resins, polyester resins, vinyl chloride-vinyl propionatecopolymerized resins, polyvinyl formal resins, polyvinyl butyral resins,polyolefin resins, and mixtures thereof.
 5. A heat-sensitive adhesivesheet of claim 1, wherein each of said synthetic resin layers contains adispersion of an ethylenic olefin-copolymerized resin, a low densitypolyolefin, a vinyl acetate-olefin copolymerized resin, an ionomerresin, or mixtures thereof.
 6. A heat-sensitive adhesive sheet of claim1, wherein each of said synthetic resin layers is a mixed resin layerformed by coating and drying a composition prepared by mixing a resindispersion selected from the group consisting of olefin-copolymerizedresin dispersions, low density polyolefin dispersions, and ionomer resindispersions, with an emulsified polyolefin resin in a mixing ratio of95:5-5:95 on a solids basis.
 7. A heat-sensitive adhesive sheet of claim1, wherein said adhesive sheet consists of said support and saidsynthetic resin layers.
 8. A heat-sensitive adhesive sheet of claim 1,wherein said support layer is a plastic laminated paper sheet.
 9. Aheat-sensitive adhesive sheet of claim 1, wherein said support layer isa synthetic resin film selected from the group consisting ofpolyethylene film, polypropylene film, polyester film, and polyamidefilm.
 10. A heat-sensitive adhesive sheet of claim 3, wherein each ofsaid synthetic resin layers has a thickness of at most about 10 microns.11. A heat-sensitive adhesive sheet according to claim 1, wherein saidsynthetic resin layers are both made of the same material.
 12. Aheat-sensitive adhesive sheet of claim 6, wherein the resin dispersionis vinyl acetate-olefin copolymerized resin dispersion.
 13. Aheat-sensitive adhesive sheet of claim 1, wherein said support layer isa cellulose triacetate film.
 14. A heat-sensitive adhesive sheet ofclaims 1, wherein said support layer is a polycarbonate film.
 15. Aninformation-recorded material comprising:at least one heat-sensitiveadhesive sheet of claim 1, which is inserted between a pair ofinformation-recorded faces of at least one sheet of recording material,wherein said adhesive sheet and pair of information-recorded faces arebonded together by heat-sensitive adhesion at a temperature of not morethan 100° C.
 16. An information-recorded material according to claim 15,wherein each of said synthetic resin layers has a thickness of at most20 microns.
 17. An information-recorded material according to claim 15,wherein said synthetic resin layers are both made of the same material.18. An information-recorded material according to claim 15, wherein asingle sheet of recorded material is folded to provide two pairs ofopposed information-recorded faces and said information-recordedmaterial contains two of said adhesive sheets, each of said adhesivesheets being inserted between a pair of opposed information-recordedfaces.
 19. An information-recorded material of claim 15, wherein saidmaterial is a postcard.